One of the important parameters influencing durability or wear resistance of mechanical devices employing a lubricating composition is the effectiveness of antiwear or extreme pressure additives at providing devices with appropriate protection under various conditions of load and speed. However, the working environment of lubricating is becoming more severe due to factors such as a size reduction of mechanical devices, or increasing speed and loads being exerted.
In order to lubricate the mechanical devices, metalworking fluids, greases and other lubricants have been formulated with additives providing extreme pressure and antiwear performance. Known additives include antimony dialkyldithiocarbamates, molybdenum sulphides (such as MoS2), phosphorus containing agents (such as zinc dialkyldithiophosphates) and boron-containing additives (such as borated esters, borated dispersants, and alkali metal borates). The alkali metal borates are commonly sold as a solid lubricant. However, the particle size of the alkali metal borates is believed to be sufficiently large thus giving a lubricant (such as a grease) a grainy appearance and with limited handle-ability. Attempts have been made to prepare a lubricant containing a dispersed alkali metal borate.
U.S. Pat. No. 5,877,129 discloses a grease composition containing a lubricant additive, wherein the lubricant additive is derived from a borate dispersion of an alkali metal salt of salicylic acid and an alkenyl succinimide. The lubricant additive provides a grease with a high dropping point and antioxidant performance.
U.S. Pat. No. 6,737,387 discloses a dispersed hydrate potassium borate composition containing a dispersant, base oil and hydrate potassium borate characterised as having a hydroxyl to boron ratio of at least 1.2:1 to about 1.5:1, a potassium to boron ratio of about 1:2.75 to 1:3.25 and a turbidity value of less than about 75 ntu.
U.S. Pat. No. 6,632,781 discloses a lubricant composition containing base oil, a dispersed hydrated alkali metal borate and a metal salt of polyisobutenyl sulphonate, wherein the polyisobutenyl moiety has a number average molecular weight of 400 to 1200.
International Application WO 00/63324 discloses a lubricant composition containing a base oil of lubricating viscosity, a dispersed hydrated alkali metal borate and a dispersant selected from the group consisting of a polyalkylene succinic anhydride and a non-nitrogen containing derivative of said polyalkylene succinic anhydride. In one embodiment the hydrated alkali metal borate is a sodium borate with a sodium to boron ratio of about 1:3.
US Patent Application 2002/0147115 discloses a lubricant composition containing a base oil of lubricating viscosity, a dispersed hydrated alkali metal borate and a dispersant selected from the group consisting of a polyalkylene succinic anhydride and a non-nitrogen containing derivative of said polyalkylene succinic anhydride. In one embodiment the hydrated alkali metal borate is a sodium borate with a sodium to boron ratio of about 1:2.5 to 1:4.5.
US Patent Application 2004/0087450 discloses lubricating an internal combustion engine with a lubricant composition containing a dispersed hydrated alkali metal borate, and at least one phosphorus-containing antiwear agent providing up to 0.08 weight percent phosphorus.
In addition, due to increasing environmental concerns and increasingly tighter health and safety legislation specifies, chemistry containing, for example, heavy metals (antimony and others), phosphorus, and sulphur are becoming less desirable.
Consequently, it would be desirable to provide a lubricating composition capable of providing at least one property including acceptable antiwear performance, and acceptable extreme pressure performance, acceptable dropping point performance, acceptable penetration (or consistency), acceptable handle-ability, acceptable environmental impact, and acceptable performance in view of health and safety legislation. The present invention provides a lubricating composition capable of providing at least one of the properties listed above. The present invention further provides methods of lubricating mechanical devices with the lubricating composition.